Radio transmitter device



RADIO TRANSMITTER DEVICE Filed 001;. 5, 1930 FIG. l

III.

FIG-.2

INVENTOR HERMAN F. MILLER,JR. BY JOHN E FARRINGTON a. ATTORNEY Patented Dec. 5, 1

TE'S

PATENT OFFICE RADIO TRAN SMITTERDEVICE Herman P. Miller, Jr., East Orange, N. J., and

John Fish Farrington, signers to International Flushing, N. Y., as- Communications Laboratories, Inc, New York, N. Y., a corporation of New York Application October 3, 1930. .Serial No. 486,162

4 Claims.

Our invention relates to radio transmitter devices, and particularly therein for stabilizing quency.

in a radio transmitter sys power dissipation inthe to :means incorporated the transmission fre- An object of our invention is to provide means tem for maintaining the vacuum tube constant over both'the marking and spacing periods, in

order to keep constant the temperature and the physical dimensions, and thereby keep constant the inter-electrode capacity and oscillation frequency.

Another object is to provide means for reducing the powerinput to spacing periods.

A further object is to a vacuum tube during provide means for stabilizing the voltage applied to the tube, and for adjusting .the power input to different values during marking and spacing periods. Still other objects of our invention are to provide means in connection with the plate power supply for. changing the eration of keying.

voltage during the op.-

.In the operation of vacuum tube-transmitters,

'- especially. at high frequencies, "where the interelectrode capacity is a capacity in the resonant substantial part of the circuit, difliculty has been'experienced in maintaining this capacity constant during signalling, because of thefact thatltheenergy dissipation theitube varies in magnitude between spacing andmarking intervals. The change inenergy dissipation in the tube results. in a change.

electrodes, which change in temperature changes the physical dimensions and inter-electrode spacing and thereby the inter-electrode capacity. This results in a change in the overall capacity in the resonant circuit, which of course changes the oscillationfrequency. The change in dissipation of energy in the or without a change in t tube may occur either with he plate current.

The frequency of oscillation not only changes with change in electrode temperature but also changes with the. applied voltage.

m a motor generator set if the tube is supplied fro Accordingly,

which changes its speed somewhat when the load is changed, an increase spacing periods, by increasing in plate current during the generator load,

may reduce its speed and'voltage, thus causing thev application of a decreasing voltage at the beginning of a marking period. While the, change in generator speed betwe spacing periods may higher frequencies of changein generator volt en marking periods and be small, nevertheless at, the generation, even a few volts age from a change ofa in temperature of the few revolutions per minute may produce a considerable number of cycles change in frequency, resulting in still further'disturbance of the frequency stability. At high frequencies and when heterodyne reception is usedthese changes are troublesome because of the change in beat note frequency in the .heterodyne' receiver, which makes the code less easy to read, as well as the reduction in signal strength from departure from exact resonance between signal and receiver.

Our invention providessimple means for adjusting the power input to the transmitter to different values during keying and spacing pericds in such a way as to maintain the energy dissipation in the tube constant, whether the tube is oscillating for a markingperiod ornon-oscillating for a spacing'period, thereby maintaining the electrode temperature and the oscillation frequency constant. In addition our invention permits of'working the tube at a higher duty-rate because of the fact that allowance does not need to be made for any greater energy dissipation in the tube than is incidental to the translation of power.- Under the older systems the tube could be loaded only to'such a point-that, when the added energy dissipationduri-ng spacing periods wasallowed for, the-temperature still would note ceed the permissible limit. Thisreduction in rated output might amount to a substantial 'portion of the total power dissipating capacity of the tube. Our invention makesit unnecessary to allow any margin of this sort, and permits the tube to be loaded during oscillating periods to its maximum permissible limits without allowance for increased dissipation during non-oscillating periods.

Other objects and structural details of our invention will be apparent from the following description when read in connection with'the accompanying drawing, wherein Fig. 1 shows a simple embodiment of our invention utilizing a relay and'resistances.

Fig. 2 shows a similar embodiment with the addition of a generator for filament heating.

Referring to Figure 1, our invention includes a vacuum-tube 1, with which is associated a tuning circuit 2, and a grid inductance 3, a grid choke 4, shunted by a chopper 5 in circuit with the contacts of a keying relay 6, for opening and closing the shunt.

Any convenient current supply may be utilized for heating the filament, such as a generator, or batteriesetc. Plate circuit power is provided from any convenient source which may be a high volt- 0 would cause the renewed oscillations to be at a 57111811138, and thereby alters the age generator 7 driven by a suitable device such as a motor 21 connected to the mains 23. A radio frequency choke coil 8 is desirably included in the generator circuit as shown to prevent the flow of stray radio frequency currents into the power supply system. A plate circuit relay 9 is also provided and connected to the key circuit in parallel with the keying relay 6. The relays 6 and 9 are operated by energy from a suitable source such as a battery 10, under the control of a key 11.

A resistance 12 is connected between the positive terminal of the generator 7 and the plate circuits of the tube 1. The positive lead of the generator 7 is also connected to the tongue of the relay 9, and the plate circuit of the tube 1 is connected to one of the relay contacts 15. A second resistance 14 is also provided, and connected between the negative terminal of the generator 7 and the other contact 16 of the relay 9.

In the operation of this embodiment of our device, closure of the key 11 energizes the relay 6, closing the shunt around the choke 4. The grid coil 3 and plate tuning circuit 2 then cause the production of marking oscillations in the tube 1 which may be broken up into pulses at an audible frequency by the chopper 5 or which may be made continuous by omitting or shorting out chopper 5. Simultaneously the relay 9 is energized, drawing the tongue against the contact 15, thus disconnecting the resistance lei from across generator 7, and short-circuiting the resistance 12, thereby applying full voltage to the tube 1 for the production of oscillations. When the key 11 is opened for a spacing period, releasing relay 6, the

grid choke l is inserted in the grid circuit of the tube 1, choking out the oscillations which otherwise would fiow to the grid, and preventing oscillation of the tube. Under these conditions, the plate current may change, and the plate dissi- 0 pation increases by an amount determined by both the change in current, if any, and the amount of energy previously delivered to the aerial. The increase in energy dissipation in the tube, raises its temperature, causing expansion of the elespatial separation of the electrodes.- This would change the interelectrode capacity, and thereby the total capacity in the resonant circuit. If the relay 6 is then reclosed for a second marking period, these changes slightly difierent frequency than the oscillations at the close of the previous marking period.

This tendency is, however, prevented by the relay 9, and its connected circuits. When the key 11 is opened, releasing the relay 6, oscillations are choked out by the choke 4. Simultaneously the relay 9 is released, opening the short-circuit around the resistance 12, thereby placing it in the plate circuit and reducing the plate voltage applied to the vacuum tube. The adjustment of resistance 12 is such that the energy dissipation in the tube is the same during spacing as during marking periods.

The insertion of the resistance 12 in the plate circuit reduces the current in the generator 7 and the load on the motor 21. This may cause a substantial change in generator speed, depending on the regulation of the driving motor, and a change in the resultant voltage of generator '7. It is of course obvious that during rapid keying, the inertia of the motor and generator armatures is suificiently great to limit the changes to comparatively small values, but also during pauses in transmission there may be sufficient time for the generator speed to attain an equilibrium value at the reduced load. This changed speed and also the voltage regulation characteristic of the generator, then is effective for the generation of a diiierent voltage at the beginning of the next marking period, which likewise tends to produce a change in frequency. This tendency toward change in oscillation frequency is most easily compensated for by maintaining the load upon the generator constant by the addition of a load through a resistance 14 as shown.

The resistance 1% is shunted across the generator terminals during spacing periods by contact of the tongue of relay 9 against the contact 16, whereby it serves to maintain the load on the generator 7 constant in order to prevent voltage variations during the spacing and keying intervals. The resistance 14 may likewise be adjusted to such a value that the current which flows through it is substantially equal to the difference in current fiowing through the spacing and marking periods.

By the construction of the device of our invention, we are thus enabled to maintain the energy tube between dissipation in the tube 1 constant through both spacing and marking periods, and thereby stabilize its oscillation frequency, and likewise we are enabled to maintain the load upon the plate generator, and its voltage, constant through the entire transmisison period, avoiding the fluctuations in speed and voltage which would otherwise occur due to the change in plate dissipation in the tube. It may be noted that the tongue and contacts of the relay 9 are connected on the positive side of the generator 7 and are accordingly at a maximum potential from ground; and from the coil of the relay. This fact necessitates care. in insulating the relay tongue and contacts, .resulting in a requirement for an expensive constructed relay. It is obvious that the relay may be placed at ground potential by inserting resistance 12 between the negative terminal of generator 7 and grounded filament connection to tube 1. Fig. 2 discloses an embodiment similar to Fig. 1, except that filament power is obtained from a three unit motor generator set, consisting of plate generator 7, motor 21 and filament generator 22, mains 23 supplying current to motor 21. The load on generator 7 being constant, the generator will cause no change in speed of the motor and consequently the voltage supplied by filament generator 22 will be constant, thus By the various embodiments of the device of our invention, we are thus enabled'to obtain a uniform dissipation of energy in a vacuum tube and avoid change of dissipation between spacing and marking periods, thereby maintaining the temperature substantially constant, which constancy materially aids in maintaining the interelectrode capacity and the oscillation frequency constant. Simultaneously, we are enabled to maintain the plate and filament generator voltages constant, thus facilitating stabilization of frequency.

Use of our invention for stabilizing the frequency of vacuum tube oscillator transmitters results in reduction of interferenceto communications on adjacent frequency channels and improves reception of signals from transmitters thus equipped.

While we have disclosed several embodiments of the device of our invention, it is possible to produce still other embodiments of the same inventive concept without departing from the spirit thereof and we desire therefore that the appended claims be limited only to the extent required by the prior art or stated therein.

We claim as our invention:

1. In a radio transmitter, the combination of an electron tube oscillation generator having coupled input and output circuits, a generator for supplying current to said output circuit, signalling means for providing marking and spacing signals, means for causing the energy dissipation in the tube to be the same during spacing as during marking periods, means controlled by the signalling means for causing the tube to cease generation of oscillations during spacing periods and to produce oscillations during marking periods, and means for equalizing the load on said supply generator during marking and spacing periods.

2. In a radio transmitter, the combination of an electron tube provided with a grid circuit and a plate circuit coupled in feed back relation for producing oscillations, a generator for supplying current to said plate circuit, means for producing marking and spacing signals, means for increasing the voltage of said current to said plate circuit during marking periods, means associated with said grid circuit for choking out oscillaelement connected to said power source and connected in and out of the plate circuit under control of the signalling means and being of such value as to cause the energy dissipation in the tube to be the same during spacing as during marking periods, and means controlled by the signalling means for causing the tube to cease generation of oscillations during spacing periods and to produce oscillations during marking periods.

4. In a radio signalling arrangement, the combination of an electron oscillation generator having coupled input and output circuits, a power source for said output circuit, signalling means for providing marking and spacing signals, a choke coil under control of the signalling means connected in the input circuit during spacing periods to cause the tube to cease generation of oscillations and removed from the input circuit during marking periods thereby allowing 

